In a conventional rack-and-pinion steering system for motor vehicles and the like, a rack bar has been employed. Recently, it has been tried to hollow the rack bar so as to make it more lightweight. In a method of manufacturing such a hollow rack bar, as disclosed in Publication of Examined Japanese Utility Model Application No. Hei 1-87335, an electric resistance welded tube or an extrusion molded steel pipe is employed and rack teeth are formed in the periphery of the tube or the steel pipe by press working. In the press working, as shown in FIG. 7, a steel pipe 50 into which a core 52 is inserted is placed between an upper and a lower metal dies and another upper metal die 58 having a rack teeth configuration is pressed on the periphery of the steel pipe 50, and thereby the rack teeth are formed.
However, such a conventional method has a problem that since the core has a central flat portion and downward slopes on both sides thereof, the diameter of a corner 60 becomes large, so that an enough thickness of a flat portion 62 cannot be obtained. Furthermore, deformation of the inner periphery of the steel pipe 50 during the press working results in close contact of the core 52 with the inner periphery of the steel pipe 50 and prevents the core 52 from being removed from the steel pipe 50.